1. Field of the Invention
The present invention relates generally to multistage arrangements for countercurrent washing or countercurrent separation. The invention relates particularly to a multistage arrangement for countercurrent separation of suspended solids, particularly crystals, by means of hydro-cyclones arranged in series one behind the other, by means of groups of several hydro-cyclones connected in parallel. The arrangement further includes pumps and pump wells and pipe lines connecting the aforementioned structural elements. In this arrangement, the washing or separating fluid is conducted in a countercurrent against the feed direction of the suspended solids and the suspended solids are treated under increased pressure and temperature.
2. Description of the Prior Art
The principal construction and the corresponding mathematical bases of such arrangements are described in "Verfahrenstechnik 8 (1974), No. 1 pages 28-31" and in the "Aufbereitungstechnik", 18th year (1977), pages 395-404. Such arrangements are also discussed in German Patent No. 30 44 617, which relates to a process for the production of terephthalic acid from dimethyl-terephthalate as an intermediate product. Further, a countercurrent separating unit is disclosed in German Patent No. 29 16 197.
In such countercurrent separators, dissolved impurities are to be separated. These impurities of the feeding suspension lie below the separation grain boundary of the hydro-cyclone. The separating fluid functioning for their separation can be of different types. For example, for this purpose, demineralized water is used. One of the considerable advantages of the hydro-cyclone known for this purpose is the fact that the solid matters present in the feeding suspension are classified and are fed corresponding to their classification to the overflow or underflow.
In many fields of application, the requirement is that the process must be operated under increased pressure and temperature. Due to process conditions, a certain range of temperature must be maintained.
It is, therefore, a primary object of the present invention to further develop an arrangement of the type described above. It is specifically an object of the present invention to provide an arrangement of the above-described type in which the cost required for the apparatus is as low as possible.